Long‐term surface application of dairy liquid manure to soil under no‐till improves carbon and nitrogen stocks.

Manure application and no‐till management improve soil quality, crop yields and C inputs, but little specific knowledge is available regarding the combined effect of long‐term dairy liquid manure (DLM) application and no‐till management on soil organic matter status and soil structure in topsoils. Here, we assess the impacts of surface‐applied DLM for a 10‐year period on soil total organic carbon (TOC) and nitrogen (TN) concentrations and stocks, on organic matter fractions and on soil physical‐structural attributes in a no‐till crop rotation system on clayey Ferralsol under no‐till crop rotation management in a subtropical climate. Four rates of DLM (0, 60, 120 and 180 m3 ha−1 year−1) were applied in a randomized block design with four replications. Soil samples were collected to calculate TOC and TN stocks to 100‐cm depth and organic matter fractions in the 0–5‐cm layer, and physical indicators of soil quality: bulk density, macroporosity and microporosity and aggregate stability. The largest DLM rates (120 and 180 m3 ha−1 year−1) added 3.8–5.8 Mg C ha−1 year−1 as manure, increased crop residue input by 0.6 Mg C ha−1 year−1, and increased TOC stock by 17% and TN stock by 27% in the top 10 cm of soil, at annual accumulation rates that averaged 0.72 Mg C ha−1 year−1 and 86 kg N ha−1 year−1. Stocks of TOC and TN in the sand‐POM (particulate organic matter) fraction under the 180 m3 ha−1 year−1 rate increased by 49 and 63%, and in the silt‐MOM (mineral‐associated organic matter) fraction by 30 and 47%, respectively. In the clay‐MOM fraction, the change in TOC was not significant, but the TN increased by 16%. Soil physical‐structural attributes (bulk density, porosity and aggregates) were improved by DLM application in the 10‐cm layer and followed the soil carbon and nitrogen increments. Overall, the DLM amendment applied on the soil surface of no‐till proved to be a strategy to ameliorate soil organic matter status, an important factor for agronomic and environmental benefits, besides improving crop biomass production. Highlights: Long‐term application of liquid manure increased concentration and stock of SOC and TN in the 0–10‐cm layer.Increases of 0.72 Mg C ha−1 year−1 and 86 kg N ha−1 year−1 were observed in the 10‐cm topsoil with manure.SOC and TN increased in the sand‐POM and silt‐MOM size fractions but not the clay‐MOM fraction.Improvements to soil physical‐structural attributes were related to organic matter changes. [ABSTRACT FROM AUTHOR]